How to append float value of into a string ?

Question

I have a float variable lng = 33.785469 and lat = 78.126548. Now can I convert them to String and append in a String variable "my_location" as "your location is \nlng = 33.785469 \nlat = 78.126548". I was trying to do this with

 char charVal[5]; //temporarily holds data from vals 
 String stringVal = ""; //data on buff is copied to this string
 dtostrf(lng , 4, 2, charVal); //4 is mininum width, 2 is precision; float value is copied onto buff
 //convert chararray to string
 for(int i=0;i<sizeof(charVal);i++)
 {
 stringVal+=charVal[i];
 }
 GPS_string = GPS_string + "Car location: \nlat:" + stringVal; 
 stringVal = "";

and it given me an error :

error: cannot convert 'String' to 'double' for argument '1' to 'char* dtostrf(double, signed char, unsigned char,

Answer 1

This has been answered in the previous question but I can repeat it here:

void loop()
{
 ...
 float latitude = 33.546600;
 float longitude = 75.456912;
 String buf;
 buf += F("your location is \nlat:");
 buf += String(latitude, 6);
 buf += F("\nlong:");
 buf += String(longitude, 6);
 Serial.println(buf);
 ...
}

An alternative is to use dtostrf() as in your snippet:

void loop()
{
 ... 
 float latitude = 33.546600;
 float longitude = 75.456912;
 const int BUF_MAX = 64;
 char buf[BUF_MAX];
 const int VAL_MAX = 16;
 char val[VAL_MAX];
 strcpy_P(buf, (const char*) F("your location is \nlat:"));
 dtostrf(latitude, 8, 6, val);
 strcat(buf, val);
 strcat_P(buf, (const char*) F("\nlong:"));
 dtostrf(longitude, 8, 6, val);
 strcat(buf, val);
 ...
}

Cheers!